This invention relates to planetary transmissions and more particularly to planetary transmissions for vehicles providing a plurality of speed ratios between an input shaft and an output shaft.
Conventionally, various planetary transmissions have been proposed which have been used with the combination of a torque converter or a fluid coupling. In such transmissions for particularly large-sized vehicles such as trucks or buses, it is desirable to provide at least four speed ratios. For this purpose, it is considered to have more speed ratios than four ratios by combining at least three sets of the single or double pinion planetary gears and selectively engaging their elements of the planetary gear sets. In combining, it is desirable to satisfy the following conditions:
1. Compared with other members the input member for transmitting the input torque is subjected to the smallest torque and is, therefore, constituted of a sun gear of small diameter.
2. The output member is adapted for transmitting the torque corresponding to the product of the input torque and the gear ratio and is, thus, constituted of a considerably large-diametered ring gear or carrier.
3. The fixed or reaction member is adapted for transmitting the torque corresponding to the product of the input torque and (output toque/input torque 1:1) thus the fixed member for a low forward speed ratio or a reverse speed ratio is constituted of the ring gear or carrier.